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Selection response and realized heritability estimate for growth were investigated in Heterobranchus bidorsalis using divergent selection for High (H) and Low (L) growth for a single generation. H.bidorsalis broodstocks from Dadinkowa dam was used to produce fingerlings in the hatchery of a commercial farm. High and low growth parents were selected in the 7 th month of grow-out in earthen pond. Twelve weeks old hatchery produced juvenile progenies from H x H, L x L and reciprocally mated (H x L and L x H) parents were reared in grow-out earthen pond. Means (±SD) of the whole weight of offspring from each group after seven months of grow-out in earthen ponds were significantly different (P<0.05) with values of 279.36±13. 73g, 264.95±15.2 g and 252.29±18.65g for the H, L and reciprocally mated H and L group respectively. Direct response to one generation of selection for the H and L growth was 5.44% and 4.78% respectively which an average of 5.11% in both groups. The average realized heritability for weight at the end of the 7 th month was 16.84%. The result indicates that the application of divergent selection for high and low growth to increase H. bidorsalis production is viable and promising. Key word: Selection response, heritability, growth, Heterobranchus bidorsalis INTRODUCTION Heterobranchus bidorsalis belongs to the family Clariidae and is one of the commercially important fish species commonly cultured in Nigeria due to its high resistance to disease, efficient utilization of various types of locally formulated fish feed and simple propagation technique (1-2) and can grow to a very large size (3-4). Artificial propagation of H. bidorsalis using different hormones and management techniques has been successfully carried out (3, 5-6). Selective breeding program has been used to improve the growth rate of many cultured fish species (7) and the response to selection for growth rate in fish and shellfishes, is much higher compared to terrestrial farm animals. This is due to the higher genetic variance (20%-30%), higher fecundity which allows for higher selection intensity, less domestication and selection in fishes (8). Response to  *Correspondence to: Akinwande, A. A, Department of Aquaculture and Fisheries, University of Ilorin, Ilorin, Kwara State, Nigeria, e-mail: akinwande_fish@yahoo.com, +2348054697342 selection has been evaluated in several farmed aquatic species. About 12-18% response to selection for growth were obtained in three strains of the channel catfish (Ictalurus punctatus) after one generation of selection (9), 14.4% in Salmon salar (10), 7-9% in the Nile tilapia (11) and 7% in Oncorhynchus mykiss (12). In shellfishes, (13) obtained a 4% increase in growth rate in the Sydney-rock oyster (Saccostrea commercalis), while the Chilean oyster (Ostrea chilesis) showed 1013% gain after one generation of selection (14). In shrimps, selection response in Kurama prawn (Marsupenaeus japonicus) was 10.7% (15), while in the Pacific White shrimp (Litopenaeus vannamei) a 21% increase in growth was observed after one generation of selection (16). In Nigeria, there is no documented report of any selection program in H. bidorsalis, hence the need to improve the growth potential of this catfish species. A selective breeding program could be carried out to develop H. bidorsalis with superior growth for aquaculture production, which necessitated this study. This present study was therefore undertaken to evaluate the response AKINWANDE A. A., et al. Trakia Journal of Sciences, Vol. 15, No 1, 2017 61 to selection and heritability estimate for growth after one generation of selection in H. bidorsalis. MATERIALS AND METHODS Establishment of foundation stock The foundation stock of H. bidorsalis used in the present study were derived from wild broodstock populations using 4males (♂) and 8females (♀)) from the DadinKowa dam in the Sahel savannah of north-eastern Nigeria. Hypophysation, artificial fertilization and larvae rearing using the wild stocks were carried out in the hatchery of a commercial catfish farm (Jigna-Eco farm Bwari, Abuja) following the method of (17) in concrete tanks with continuouswater flow through system. Swim up fry were fed ad-libitum manually with shell free Artemia for, the first 21 days followed by 0.5mm-1.2mm commercial Coppen’s floating feed (42% crude protein, 13%crude fat, 1.8% crude fibre, 7.7% crude ash, 1.1% phosphorus, 1.9% calcium and 0.2% magnesium) for another nine weeks. After twelve weeks, about 600 juveniles were stocked (5fish/m 2 ) in an earthen pond (10m x 12m x1m) and fed 40% crude protein pelleted diet (1mm-3mm size) twice daily at 5% biomass. The fishes were harvested at the end of the 7 th month and broodstocks which were used as the founder stock in this study were selected. The cutoff weight for selection was obtained by individually weighing 114 fishes sampled during the harvest. Due to limited grow-out and nursery facilities, 31.57% of the harvested fishes which serves as the parent broodstocks (n=36) were selected to initiate the High line (9H♂: 9H♀) and Low line (9L♂: 9L♀) parents, while additional 16 fishes were also randomly selected and used for artificial propagation between the reciprocal High and Low lines parents (4H♂ x 4L♀; 4L♂ x 4H♂). All the fishes were individually tagged and restocked in the earthen pond (4m x5m x 1m) for another 8 months when they have become sexually matured. Experimental procedure and larval rearing Hypophysation and artificial fertilization was carried out using 1♂ and 1♀ in each of the selected parent male and female broodstocks and a total of 8HH, 8LL, 4HL and 4LH families were produced in the F1. Larval rearing was the same as previously described by (17). Swim up fry were fed ad-libitum manually, with shell free Artemia for the first 21 days followed by 0.5mm-1.2mm commercial Coppen’s floating feed (42% crude protein, 13% crude fat, 1.8% crude fibre, 7.7% crude ash, 1.1% phosphorus, 1.9% calcium and 0.2% magnesium) for another nine weeks. At the 10 th week of larval rearing, fingerlings that appeared too large (>21g) or too small (<11g) based on average weight of the whole population (16.0±5g) were removed so that it does not introduce bias in the selection of progeny for grow-out. At 12weeks of age 60 juveniles from each family in the different groups were divided into triplicates and stocked in small net cages (2mx2mx1m) suspended in earthen pond (10m x 12m x 1m) with the bottom of the net touching the substratum. The sizes of the juveniles were carefully selected so as to match the size distribution of the overall population in the tank from which they were selected. The same stocking density of 5fish/m 2 used for the stocking of the parents in the grow-out pond as earlier mentioned was also applied. All the F1 progenies from the different groups (genotypes) were raised in separate net cages for the first two months of culture, after which they were removed and individually tagged using PIT tag, and then directly stocked together in the same ponds, since communal stocking such as this will reduce the environmental component of variation. Data collection The F1 progenies in each net cages for the different groups for the 7 months of grow-out were weighed monthly and recorded. Mortality was also recorded while dead fishes were not replaced. The monthly weight of the selected parental from the end of the 7 th month till the 15 th month in earthen pond when they were removed and used for production of the F1 were also recorded and feed rations were adjusted monthly with the weight increase. Selection response for one generation of selection was calculated using the equation of (18) : S. R(%) = HH or LL−HL and LH x 100 HH and LH Where HH and LL are mean growth of the selected High and Low progenies (F1) respectively, HL and LH are the mean growth of the reciprocals mated High and Low progenies. Selection differential was calculated using the equation of (18): S.D = XF XF0. Where XF is the mean body weight of the selected parents and XF0is the parental population mean. Realized heritability was calculated based on (18) equation as: h 2

Selection response and heritabilityestimate for growth in the giant african catfish ( Heterobranchus bidorsalis Geoffroy Saint-Hilaire, 1809 )